[Pierre Farrugia]

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<font color='#0000FF'>Hello,

I always wondered how to use air breaks due to CNS in a dive plan. Let say you have 50min on O2, so you have to introduce air breaks. Do you use decompression software to cater for it? or you just get them in your profile? My big

? is, if the software says you need 50min on pure O2 and you spend 5min of them on air as air break, would it be that you will not off gassed as the software would have calc. and thus making you prone for a hit? Also if you dive a hypoxic gas, on what you do your air break? If diving with travel 32% is it useful? Also while a DIR dive what you use?

regards

Pierre Farrugia

 

[Phil Ennis]

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<font color='#810541'>Pierre, you might be better off posting this on the DIR forum, I think you will possibly get more response.

 

[Mark Chase]

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Air breaks are Vodo

There is no science to it.

The basic principle is afterpassing 80% CNS or 20mins on 02 you should incorperate 5min air breaks into deco to avoid a CNS hit. More importantly pure 02 fries your lungs so an air break to prevent this is a good thing.

Air breaks are basicly in two forms. Their is the 15mins on 02 and 5 on Trimix crew and there are the 20mins and 5 mins on Trimix crew. Long and short of it is, if you plan to pass 100cns on your dive: Plan every detail in advance

ATB

Mark Chase

 

[Andy Phillips]

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To add to Marks bit, when I asked this question some time ago when I was deciding what gas to use for deco (80 or 100%) I was told that the air breaks are discounted i.e. when on the air break you are considered as far as the deco is concerned to be neither on nor off-gassing. As Mark said, voodoo, in fact a bit scary. Hence why a lot of the guys who do the very long deco times use a habitat or a full face mask for the 100% stage of the deco.

Andrew

 

[Tibbs]

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Quote[/b] (Mark Chase @ Sep. 14 2003,22:16)]Air breaks are Vodo

There is no science to it.

The basic principle is afterpassing 80% CNS or 20mins on 02 you should incorperate 5min air breaks into deco to avoid a CNS hit. More importantly pure 02 fries your lungs so an air break to prevent this is a good thing.

Air breaks are basicly in two forms. Their is the 15mins on 02 and 5 on Trimix crew and there are the 20mins and 5 mins on Trimix crew. Long and short of it is, if you plan to pass 100cns on your dive: Plan every detail in advance

ATB

Mark Chase

The WKPP use 12 minutes on and 6 minutes off. They manage to run their CNS clock into the thousands because 6 minutes on Back Gas essentially 'resets' the clock. It also maintains lung capacity, which is very important too.

Andrew Georgitsis (GUE Training Director) who dives extensively off Seattle has been talking to the Chamber in Seattle who have started to use 12 on 6 off with their bends patients and have noticed a reduction in damage to lung tissue and an improved recovery rate.

Pure O2 doesn't fry your lungs. Breathing a high PPO2 fries your lungs. How did bomber crews during WWII do hours and hours in the air on Pure O2 without toxing? Breathing 80% at 1.6 will fry your lungs just as quickly as breathing O2 at 1.6. This is also why that GUE deco gasses are a max PPO2 of 1.4 deeper than the 50% bottle.

Chris

 

[Mark Chase]

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Quote[/b] (Tibbs @ Sep. 14 2003,22:25)]

Quote[/b] ]The WKPP use 12 minutes on and 6 minutes off. They manage to run their CNS clock into the thousands because 6 minutes on Back Gas essentially 'resets' the clock. It also maintains lung capacity, which is very important too.

I have a BIG problem with the misconception that air breaks re set the CNS clock. They dont. It takes aproxamatly 10 hours breathing air at atmospheric presure to re set the clock. 5min air breaks reduce it by a few percent but actualy do very little to help with CNS. The main reasion air breaks are valuble is that 02 at high partial preasure will cause a reaction in the lung resulting in swelling and the development of meucus on the tisue that restricts the effect of off gassing. The air breaks greatly reduce this affect and promote better transfer of nitrogen.

Quote[/b] ]Pure O2 doesn't fry your lungs. Breathing a high PPO2 fries your lungs. How did bomber crews during WWII do hours and hours in the air on Pure O2 without toxing? Breathing 80% at 1.6 will fry your lungs just as quickly as breathing O2 at 1.6. This is also why that GUE deco gasses are a max PPO2 of 1.4 deeper than the 50% bottle.

Chris

This is quite true but you dont breath 80% at 1.6 for long usualy 5 mins mabey 10 on a deep dive. The 6mstop will be at a PP02 of 1.29 which greatly reduces CNS exposure and limits the effect of deco dammage to the lung. Even after 81mins of deco comming up from 60m you are still well below the 80% threshhold for air breaks. If you use 100 % you would need to extend your deco by 12mins (using 6 & 12) and add two air breaks to your 6m profile resulting in a run time of 92mins for deco.

ATB

Mark Chase

 

[Dominic]

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ISTR that air breaks are considered part of the 100% stop - you don't spend any extra time at a stop because of air breaks.

 

[Mark Chase]

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Quote[/b] (Dominic @ Sep. 15 2003,13:38)]ISTR that air breaks are considered part of the 100% stop - you don't spend any extra time at a stop because of air breaks.

Dom

I spent a lot of time reserching air breaks for my Illinoys dive and there are definatly two schools of thaught on the air breaks. Some say add them to deco time some say dont bother. The dont bother mob are seen as a bit gung ho. doing long hangs and taking several air breaks could potentialy be a shed load of missed stop time. Whilst the on gassing during air breaks is ignored because they recommend using Trimix to reduce the nitrogen it is also a period where no off gassing is occuring. So in theroy you are loosing 6mins off gassing time every time.

The new concept (from JJ / DIR) is that air breaks improve the eficiency of deco so much that the stops can be greatly reduced. However for this to work you would have to be folowing the use of trimix as a deco gas and trimix in air breaks. Using normal air or low percentage nitrox for air breaks and standard Nitrox as travle gas, I would strongly recommend adding air breaks to total deco untill a load more reserch is done.

ATB

Mark Chase

 

[And]

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<font color='#0000FF'>Hi

The WKPP use a 12 minutes on 6 minutes off routine. It is not breaks on air it is breaks on backgas which will be a lower po2 than air. The break time is included in the stop as far as I know.

I do not know whether this practice 'resets' the clock and I believe that is just an attempt at explaining what is a complicated phenomenon. As far as I am aware the CNS clock is theoretical and not fully understood (which to me means there simply is no such thing as a CNS clock

). The term clock seems to point to time as the constraint or trigger whereas in truth current research and results are pointing more to a combination of time and constant high po2 level.

There is nothing to say you will get a CNS hit after 5 minutes or 50 minutes and you may get a hit one day and not the next and so how do you know where you are on this 'clock' ? All they do know is that below 1.4 there is little chance of a hit. Note that does not include the 1.6 deco limit, that is only under 1.4.

What I do know is what has worked in the real world. DIR and WKPP use standard gasses and use low pO2 during the dive well below 1.4. They also do not elevate the po2 until at 20 mtrs and then they only ever breath O2 for 12 minutes on and 6 off. This has allowed many dives which run into 1000's on the theoretical 'clock' and this evidence is enough for me to treat this theory with extreme scepticism. The concern now is to reduce pulmonary toxicity so as not to permanently damage the lungs.

I am more of the opinion that the breaks somehow fool your body as they effectively lower the O2 intensity enough so that you can breath O2 again without CNS penalty therefore meaning that you never reach the 'limit' as it were. They also reduce the pulmonary problems mentioned above.

IMHO

Andy

 

[Pierre Farrugia]

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<font color='#0000FF'>Hello,

Very interesting read from all of you  

 So what times are used in air breaks 12m O2 and 6min bottom gas, 20min O2 and 5min bottom, are there any other times? Also anyone here have any profiles of such dives? If the any spftware which takes care such breaks?

Also what you use if backgas is hypoxic as the deeper the more deco you have and at 6m a deep mix does not have enough O2.

Regards

Pierre Farrugia

 

[Dominic]

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Maybe they figure that since you're trying to get rid of the excess Oxygen, breathing a hypoxic mix will just use up the O2 sitting in your body and therefore presents no risk?

 

[Mark Chase]

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It is unlikley that the back gas will be hypoxic even 12/80 would be breathable at 6m because you are at 1.6 atms so it would be tha same as breathing 19% at the surface. When you start droping below 110m it might be considered a problem but I think even 10/80 is breathable at 6 (just) as long as you are not exerting your self so that will get you to 130m.

The only thing I know that does air breaks is the VR3 computer (which prompts them after 80% CNS is reached) and the proplanner that goes with it. Also Vplanner which is a free down load will incorperate air breaks into the profile.

ATB

Mark Chase

 

[MartinS]

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Hi Mark
When doing air breaks on the VR3, I guess you do a gas switch on the computer to air for the duration of the break - have you done any comparison dives without air breaks to see what difference to the deco time it gives, or is reducing deco time not appropriate with air breaks, just stopping the long exposures to high ppO2 the only need to do them.
Sorry if this sounds a silly question - just want to understand more of the sort of diving you do, and I hope to be doing someday.
Regards, and dive safe
Martin

 

[Mark Chase]

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Thats a tough question.

Problem is the VR3 will recommend air breaks as soon as you hit 80% CNS and I am not aware of a way of switching that system off.

The other problem is that you always get a shorter run time on the VR3 than on tables because the VR3 plans deco on what actualy took place and the tables are usualy bassed on max depth or max less about 3m for the end of the dive. As a result any comparison has to be maped with a complicated multilevel profile after the event using the data provided by the VR3.

Surfice as to say I have never bothered doing it

I would add the air breaks to my 6m stop and thats that. If I was on a VR3 and folowing that (asuming my buddy has another VR3 for cros referance or I have two VR3s) I would just do what it told me and kick it arround the room later if it got me bent. At the moment if I am going to do air breaks I would run tables as I havent had enough experaince with the VR3 to trust it that much.

Lets face it, if the dive is such that it warrents exceading the CNS recomendations and risking a CNS hit, who cares about another 15mins in the water if it ensures your wellbeing? A big dive like that is a dangerous thing and I for one dont want to screw up on the easy bit where you just hang in 6m of water doing nothing.

ATB

Mark Chase

 

[Pierre Farrugia]

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<font color='#0000FF'>Hello Mark,

Quote[/b] ] I would just do what it told me and kick it arround the room later if it got me bent

I like this comment  

Mark which copy do you have a ProPlanner ? I have 7.12C

 

[db8us]

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Hi Dudes,

we have some profiles on www.ekpp.org i also posted some here in the forum a few months ago.
Since 2-3 years i do not even calculate the CNS% any longer, because i think they are ok for nitroxdives etc , but not for longish cave-dives. we lower the pO2 in the bottom-time an extended our breakes to 12m on O2 and 8Min off without adding them to the decotime, so the deco stays short.
This is working IMHO with High-He mixes and not with Air/Nitrox-dives...

 

[TDave]

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Quote[/b] (Mark Chase @ Sep. 15 2003,17:12)]At the moment if I am going to do air breaks I would run tables as I havent had enough experaince with the VR3 to trust it that much.

Why spend X amount of hard-earned pounds on it then?

 

[Phil Ennis]

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<font color='#0000FF'>Because you don't have to be doing air breaks to use a VR3.

How many air breaks have you done?

Get your fuc*ing hair cut.

 

[Mark Chase]

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Quote[/b] (TDave @ April 18 2004,00:15)]

Quote[/b] (Mark Chase @ Sep. 15 2003,17:12)]At the moment if I am going to do air breaks I would run tables as I havent had enough experaince with the VR3 to trust it that much.

Why spend X amount of hard-earned pounds on it then?

As Phill said you dont have to do the air breaks recomended by the VR3, but the key word you missed was experance. When I wrote that post (Sep 03) I had only done 6 dives on the VR3 and I was still running tables side by side to ceck it was working corectly.

I have now loged 36 dives with the deepest down to 102m on the VR3 and I quite litraly trust it with my life  

I am frankley astonished that any one not limited by the doctrins of DIR or lack of free cash would do Trimix diving without one. They are great bits of kit.

Since writing that post I have made a concious decision to keep CNS down by lowering PP02 at max depth and using 80% for deco. If I do run air breaks I will add them to the total 6m stop time and run 5 in 15min profiles.

ATB

Mark Chase

 

[TDave]

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Phil, you already know I haven't done any air breaks, or dives requiring them, but my question didn't regard that.

My question was aimed more at the element of trust, although, as pointed out, I did fail to pay attention to the date of the original post - problem with posting late at night! - and Mark says he does now trust it completely, which to be honest is what I would expect, and makes sense. And that's fine and answers my question!

TD